The vapor vent valve assembly provided on current automotive fuel tanks typically has a fixed fuel vapor vent orifice to provide a flow passage from the fuel tank vapor space or dome to an emission apparatus, such as a charcoal canister, located external of the fuel tank. Fuel vapor vent valve assemblies typically are designed with a mechanism to close the fuel vapor vent orifice in the presence of liquid fuel, such as may occur at high static fuel levels in the fuel tank and from sloshing fuel in the fuel tank during vehicle movement. Closure of the fuel vapor vent orifice typically in the presence of liquid fuel at the valve assembly has been effected by a float biased with a spring load as required to achieve a buoyant force responsive to both static and dynamic fuel level changes. For instance, the float can have its upper region configured to include a nipple that is seated against the vent orifice to provide a liquid/vapor tight closure of the fuel vapor flow passage leading from the vent orifice to the charcoal canister.
During dynamic fuel sloshing conditions occurring during vehicle maneuvers, the float nipple seats against the entrance to the vent orifice when the fuel level is above the float buoyant point and is supposed to unseat when fuel level is below the buoyant point. However, a functional problem has been encountered with respect to valve unseating when the vent orifice is closed during high fuel levels that cause increased fuel tank vapor pressure and an increased pressure differential across the closed valve/vent orifice. In particular, the downward force required to reopen the fuel vapor vent valve is defined by and limited to the effective weight of the float (actual weight minus spring load and, if any, liquid buoyancy force). Therefore, it is possible that the effective weight of the float may be insufficient to counteract the vent orifice closure force resulting from the tank vapor pressure multiplied by the orifice sealing area. This adverse float weight condition has occurred when the vent orifice is designed to be large to accommodate high fuel vapor flow rates to minimize tank pressures pursuant to vehicle manufacturer requirements and the overall vent valve assembly size is insufficient to permit use of a float with a weight as required to reopen a closed (sealed) vent orifice at a specified level of fuel tank pressure due to vehicle manufacturer packaging envelop/space constraints on the fuel tank.
An object of the present invention is to provide a vapor vent valve assembly for a vehicle fuel tank that overcomes this problem of valve reopening.
Still another object of the present invention is to provide a vapor vent valve assembly for a vehicle fuel tank that overcomes this problem of valve reopening as exacerbated by high fuel vapor flow rate requirements and by limited packaging envelop/space constraints on the fuel vapor vent valve assembly.
A further object of the present invention is to provide a vapor vent valve assembly for a vehicle fuel tank that overcomes this problem of valve reopening by virtue of including a rotate-in-seat vent valve mechanism.